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Wireless Lan Error Correction

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Anonymous
a b F Wireless
August 20, 2004 8:55:03 AM

Archived from groups: alt.internet.wireless (More info?)

Hi,


My wireless setup is :

NetGear WGT634u 108 mbps wireless router with 4 10/100 ethernet ports

Netgear WG511T 108 mbps PCMCIA wireless network card

I use these for playing games on the lan and surfing the net.

Ive never had any problems with quake3 operation flashpoint on the
lan.

However while downloading from the internet across the wireless
network it always fails after a few miutes (randomly). Also if i try
and play a snooker game against someone on the internet it fails after
a random period too.

I assume error correction is the problem.
I have an excellent signal strength on the laptop.


Any ideas ?


Damo784
Anonymous
a b F Wireless
August 20, 2004 12:45:05 PM

Archived from groups: alt.internet.wireless (More info?)

On 20 Aug 2004 04:55:03 -0700, damienfitzgerald@vodafone.ie (Damo784)
wrote:

>My wireless setup is :
>NetGear WGT634u 108 mbps wireless router with 4 10/100 ethernet ports
>Netgear WG511T 108 mbps PCMCIA wireless network card
>I use these for playing games on the lan and surfing the net.
>Ive never had any problems with quake3 operation flashpoint on the
>lan.
>
>However while downloading from the internet across the wireless
>network it always fails after a few miutes (randomly). Also if i try
>and play a snooker game against someone on the internet it fails after
>a random period too.
>
>I assume error correction is the problem.
>I have an excellent signal strength on the laptop.

Assumption, the mother of all screwups.

There is no error correction. There is error detection and resend the
packets at the TCP level. However that only works with TCP, not UDP
which does not require an acknowledgement. If your online games are
UDP or multicast, there is no resend. If something causes your
wireless device to lose connection long enough for a timeout, it just
gives up.

The two times I troubleshot one of these "random" errors, I traced it
down to RF interference. The first was from a neighbors microwave
oven. The 2nd was from a cordless phone. Look in the log file on the
router to see if there are any clues as to timing and signal loss. I
would normally suggest a complicated method of interference detection
using directional antennas and a spectrum analyzer. However, both of
these were discovered with simple observation.

Speaking of interference, I'm suppose to troubleshoot wireless
"connectivity problems" in the cafeteria area of an office building
where about 6ea microwave ovens operate almost continuously during
lunch time. People are complaining that they can't reliably use the
corporate wireless network in the cafeteria. They already suspect the
microwave ovens but want to know if I can do something about it.
Maybe some of that WiFi absorbent wallpaper. Sigh.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
August 20, 2004 10:44:16 PM

Archived from groups: alt.internet.wireless (More info?)

"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
news:l36ci094a29l91il4l0js46jag08je9cn8@4ax.com...
[snip]

> Speaking of interference, I'm suppose to troubleshoot wireless
> "connectivity problems" in the cafeteria area of an office building
> where about 6ea microwave ovens operate almost continuously during
> lunch time. People are complaining that they can't reliably use the
> corporate wireless network in the cafeteria. They already suspect the
> microwave ovens but want to know if I can do something about it.
> Maybe some of that WiFi absorbent wallpaper. Sigh.

Jeff,

You're not far off: at building I worked in once, we wound up constructing a
Faraday Cage around the microwaves in the cafeteria, and it was very
effective at eliminating stray radiation into the eating area.

This was a bit before WiFi: they were concerned about possible interference
with cardiac pacemakers.

William
Related resources
Anonymous
a b F Wireless
August 20, 2004 10:44:17 PM

Archived from groups: alt.internet.wireless (More info?)

<<<<<<<<<<<There is no error correction. There is error detection and
resend the
packets at the TCP level. However that only works with TCP, not UDP
which does not require an acknowledgement. If your online games are
UDP or multicast, there is no resend. If something causes your
wireless device to lose connection long enough for a timeout, it just
gives up>>>>>>>>>>>>>


This is very interesting.

I have 2 questions

1) When downloading an application does it use tcp?
Because as i said the download keeps stooping after a few minutes.

2) Is there not any sotware that i could install at the pc (Gateway to
the internet ) that is physically connected to the router and also
software that would be installed on the wireless laptop that would
monitor data that was sent to it?

So say for example between these two it would use its own tcp protocol
(even if the snooker game was using udp )and could there for request
the gateway pc to resend the data.

Damo784
Anonymous
a b F Wireless
August 21, 2004 6:41:06 AM

Archived from groups: alt.internet.wireless (More info?)

On 20 Aug 2004 16:14:45 -0700, damienfitzgerald@vodafone.ie (Damo784)
wrote:

><<<<<<<<<<<There is no error correction. There is error detection and
>resend the
>packets at the TCP level. However that only works with TCP, not UDP
>which does not require an acknowledgement. If your online games are
>UDP or multicast, there is no resend. If something causes your
>wireless device to lose connection long enough for a timeout, it just
>gives up>>>>>>>>>>>>>

>1) When downloading an application does it use tcp?
>Because as i said the download keeps stooping after a few minutes.

HTTP and ftp downloads both use TCP. Streaming audio, VoIP, and
anything that's time sensitive, uses UDP. You can get a good idea of
which protocols use which flavour by looking in the file:
c:\windoze\services
The full list is at:
http://www.iana.org/assignments/port-numbers
Just search for your favorite application.

If you're downloading using a web browser or ftp client, it most
assuredly uses TCP. That means the server demands ACK's before
continueing to spew packets in your direction. For most systems
(except Satellite ISP's), the server will send 64Kbytes worth of
packets before it waits for ACK's.

To insure maximum confusion, many protocols use both TCP and UDP. In
general, UDP is used for the time sensitive streaming, while TCP is
used as a control channel.

What usually happens is that your wireless link goes dead for a while
thanks to interference. Eventually, it recovers and the download
continues. However, if the interruption is too long, the server will
timeout and stop sending. There are protocols that work around this
effect (Bittorrent, FastTrack, P2Pism, and various peer-to-peer
protocols). However, if you're getting a "connection reset by peer"
message, your connection was lost. Incidentally, traffic doesn't need
to totally stop to generate a reset. I merely needs to have a high
enough packet loss that an excessive number of resends are generated.

>2) Is there not any sotware that i could install at the pc (Gateway to
>the internet ) that is physically connected to the router and also
>software that would be installed on the wireless laptop that would
>monitor data that was sent to it?

Sure. SNMP will disclose both the type of errors and keep a count.
MRTG will display a pretty graph of the damage. Ideally, you would
want an access point and client radio that both can do SNMP. Few of
the cheap radios have SNMP and the few that do (DLink DWL-900AP+)
don't have MIB's to decode the garbage. Most Lucent/Orinocco/Proxim
hardware does have a nice SNMP stack.

See:

http://groups.google.com/groups?selm=85nih0d5oem1s6lbqg...
for some drivel I posted on the subject.

There are other stand alone utilities that basically do the same thing
on the PC. However, these will not show errors at the MAC (radio)
level as SNMP will.

>So say for example between these two it would use its own tcp protocol
>(even if the snooker game was using udp )and could there for request
>the gateway pc to resend the data.

I have no idea what your game runs. When your game is running, open
an MSDOS window on your computah:
Run -> cmd (W2K and XP)
Run -> command (W95/98/ME)
and run:
netstat -n (protocols and ports used by IP address)
netstat (same but with DNS names)
netstat -e (errors)
The protocol (TCP/UDP/ICMP) is in the "Proto" column.

However, fixing an what I'm *GUESSING* is an interference problem by
messing with the protocol pile is not my idea of the right way to do
things. Try to find out why the downloads stop, and work on fixing
the problem at the source. Then, if that fails, do the protocol
exercises.



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
# 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
!